Molybdenum compounds are well known for improving the properties of lubricating oils for internal combustion engines. Lubricating oils containing soluble molybdenum are known for reducing friction between moving parts in internal combustion engines, thereby improving fuel economy and increasing engine life through reduced wear.
A great number of hydrocarbon-soluble molybdenum containing compositions have been disclosed in the art, including water soluble molybdenum-amine complexes, W. F. Marzluff, Inorg. Chem. 3, 345 (1964), molybdenum-oxazoline complexes, U.S. Pat. No. 4,176,074 Coupland, et al., and molybdenum lactone oxazoline complexes, U.S. Pat. No. 4,176,073 Ryer, et al., molybdenum beta-keto esters, molybdenum-olefin-carbonyl complexes, molybdenum-amide complexes, molybdenum diorganophosphates, U.S. Pat. No. 4,178,258 Papay, et al., molybdenum organodithiophosphates, molybdenum carboxylates, molybdenum dithiocarbamates, etc.
A series of patents issued to King and de Vries, and assigned to Chevron Research Company in 1981, disclose lubricating oil compositions incorporating antioxidant molybdenum compounds, these patents being U.S. Pat. Nos. 4,259,194, 4,259,195, 4,261,843, 4,263,152, 4,265,773, 4,272,387, 4,283,295, and 4,285,822. The inventors state that the precise molecular formula of these molybdenum compounds is not known, but they are believed to be compounds with molybdenum oxides or sulfides complexed by or the salt of one or more nitrogen atoms from a basic nitrogen-containing composition (such as e.g., succinimide, carboxylic acid amide and Mannich bases) used to prepare the lubricant. A polar promoter to facilitate the interaction between the acidic molybdenum compound and basic nitrogen compound may be used, preferably ethylene glycol or water.
U.S. Pat. No. 4,266,945, Karn, discloses a friction modifying lubricant prepared by the reaction of an acid of molybdenum or salt thereof with a phenol or aldehyde condensation production and a primary or secondary amine. The compositions are stated to be especially useful when combined with active sulfur and an oil-soluble dispersant. In U.S. Pat. No. 4,202,781, Sabol, et al., a method of preparing a molybdenum phosphosulfurized hydrocarbon composition is disclosed, the composition being useful as an oxidation inhibitor and friction modifier for lubricants of internal combustion engines. The reaction disclosed produces stable molybdenum-containing compositions without high temperatures, the use of ketone or ether-complexing solvents, or hydrogen peroxide.
U.S. Pat. No. 3,047,500, Matson, discloses what the patentees believe to be a molybdenum sulfide formed in situ as a result of the interaction of a molybdenum phenolate and an oil-soluble organic sulfur compound. These two ingredients are added to a lubricant for extreme pressure protection, there being no chemical interaction between the molybdenum and sulfur until substantial heat has been generated on the worked surfaces to produce the molybdenum sulfide.
The molybdenum compounds produced by the methods of the above-noted patents, all of which are expressly incorporated by reference herein, potentially suffer from either economic inefficiencies or from changing product requirements. For instance, the additive of the Sabol, et al. patent has found widespread commercial acceptance as a friction reducing component of lubricating oils. Unfortunately, it contains phosphorus, a component which, when introduced into an automobile exhaust system, can adversely affect the efficiency of various air pollution control devices, such as, for instance, catalytic convertors and oxygen sensors. For this reason, at least one major U.S. automobile manufacturer has specified a maximum level of 0.11% phosphorus in motor oils for 1983 and thereafter. The most effective anti-wear component in most oil additive packages is zinc dithiophosphate, and at current levels of incorporation in motor oils, would effectively use up the entire phosphorus "allotment." Therefore, there is an urgent need for a commercially acceptable molybdenum additive which is an effective friction-reducing agent in motor oil without the use of phosphorus.